Methods for producing aerated fat based products are known. For instance, EP 0 322952 B1 relates to aerated ice confections and aerated chilled confections. Chocolate or suitable vegetable fat containing material is melted in a container, tempered and pumped by a pump to a mixer and pressurized CO2 is supplied to the mixer and the molten chocolate is dispensed by a dispenser having a dispensing valve. When the dispensing device is put in the non-dispensing position, the chocolate is recirculated through a backpressure valve, through degasifying means, such as a static mixer, to the container. Accurate control of the amount of product deposited is difficult due to the product velocity in the lines and requires anticipation of the deposited volumes. Furthermore, this process is complex and energy consuming, as it requires a recirculation of the chocolate and degasification of the recirculated chocolate.
WO 94/19963 relates to a method for dispensing an aerated composition comprising the step of: (a) introducing the composition under pressure into a first volume, (b) allowing the first volume to expand to a second volume at which the pressure of aeration is ambient, and (c) dispensing the second volume of aerated composition.
W002/13618 relates to a method for making a cellular food product, by dispersing and/or dissolving under pressure a gas in a food product comprising at least a butterfat, then by expansion to produce cell-formation. The method involves depositing a cellular food product in the form of individual products, or at least strip, whereof the shape is globally preserved as long as it is not subjected to a compression force. The pressure is progressively reduced along the line thereby causing the product to expand before it is deposited.
U.S. Pat. No. 4,637,788 relates to a valve type depositor for depositing an aerated confection. The valve opens and closes to deposit material. Pressure is released on the exit of the valve. The pressure of the system is held constant by always having the same number of valves open. Therefore, there is always material being deposited from some part of the depositor system. The system described in U.S. Pat. No. 4,637,788 does not have the ability to deposit along the full length of all moulds. The depositing system described herein relies on depositing material at some point of the mould and subsequently redistributing the material by vibrating the moulds. This leads to uneven bubble structure along the product and important loss of aeration.
The present invention aims at proposing a solution for depositing a pumpable product which contains gas while accurately controlling weight and volume of the deposited mass and uniformity of the foam produced.
For that, the invention relates to a depositing device for depositing flowable food containing gas comprising
a pressurized feed line conveying flowable food containing gas under pressure into the food
piston means operatively connected to the feed line comprising a piston and a chamber;
an outlet to deliver food at the atmospheric pressure into moulds. An improvement of the depositing device is to have pressure retaining means arranged with the piston means to fill the piston means with pumpable product whereas the product in the filled chamber is maintained at the line pressure. This keeps the food under pressure until the point at which it is deposited. This largely maintains the gas within the food so that the food is not in an aerated form. The bubbles only form as the food enters the mould. From then on, there is less physical action on the bubbles to distort them. Therefore, the benefit of maintaining the filled chamber at the line pressure is that it ensures the gas remains in solution so that the depositing mechanism is dealing with a liquid not a foam guaranteeing the correct weight and volume of product delivered. In other words, the gassed product in the chamber is not given the possibility to expand in the chamber in an uncontrolled manner which would, at the time of depositing in the mould leads to dosing accuracy problems, gas pockets or lack of uniform size distribution of the bubbles.
More particularly, a pressure retaining means is arranged to retain the product in the chamber at the same pressure as the line pressure and deliver the product through the outlet as pressure in the chamber increases from the line pressure upon descent of the piston in the chamber. The pressure retaining means ensures that the filled chamber is maintained at super-pressure where the gas remains substantially in the dissolved state of transport but also allows the product to be discharged once the pressure exceeds a certain threshold by the effect of the piston descending into the chamber.
The pressure retaining means can be a pressure-actuated valve arranged at the outlet. This solution is simple and reliable. Therefore, the valve automatically opens when the pressure exceeds the line pressure by a certain threshold value. It ensures that the pressure is retained in the piston means which maintains the gas inside the product until the piston means is activated for dispensing, so no specific control of the opening of the valve is necessary. Preferably, the pressure-actuated valve could be a spring-loaded nozzle. Preferably, the valve can be calibrated to open at a pressure of more than 0.5 bars above the line pressure. Therefore, this guarantees that it is only at the point of entry into the mould that the pressure decreases and the chocolate starts to expand.
The line pressure may be preferably maintained at a pressure of between 2 to 30 bars, preferably 6 to 15 bars. Therefore, the product delivered to the piston means is always fresh and has the correct quantity of gas.
Another improvement is to have a second valve means which is arranged between the feed line and the chamber and which operates between an opening position wherein the chamber is filled with flowable food and a closed position wherein the chamber is isolated from the feed line. The second valve means ensures the chamber is hermetically closed after filling while the pressure inside the chamber is maintained. Therefore, depending on the seal properties of the valve, no gas or, at most, very small amounts of gas can escape out of the chamber back to the feed line when pressure exceeds the feed line pressure once piston starts its descent.
In a preferred embodiment, the valve at the feed line has a rotary valve bar comprising at least one passage upon rotation of the valve at a coinciding position between the feed line and the chamber and has a sealing surface extending along an angular path of at least 90 degrees, preferably 130 degrees, most preferably of 180 degrees. A rotary valve has the advantage to require low force to activate between the open and close position and it furthermore provides an extensive sealing surface that ensures no gas loss and sedimentation problems. Sediment problems are caused by the solid particles of the chocolate building up between the body or housing and the rotating valve bar.
In a preferred embodiment, the invention also relates to a device for producing food containing gaseous bubbles from a pumpable product comprising:
a plurality of depositing devices as aforementioned,
a feed line for conveying the pumpable product to the depositing devices,
pump means for providing speed to the pumpable product through the feed line,
a source of gas for incorporating gas into the pumpable product and connected to the feed line,
the pump means being arranged to draw off gas from the gas source and control gas intake into the feed line by the control of the speed of the pump means.
As opposed to prior art devices, pump means are disposed for transporting the pumpable product and utilized to regulate the gas intake into the system. More particularly, the pump means comprises a first and second pumps arranged in series along a portion of the feed line. The line pressure is generated entirely by the first pump whereas the second pump controls the gas flow into the region between the two pumps. In particular, the line pressure is substantially maintained at a constant value from the exit of the first pump to the depositing devices to ensure that the product does not expand in the line before it is deposited.
The first and second pumps are driven at relative different speeds to create a suction effect within the portion of the feed line. Therefore, the second pump is driven at a speed higher than the speed of the first pump thereby incorporating gas into the portion of the feed line at a point upstream the second pump. As a result, while the first pump ensures accurate metering of the pumpable product through the feed line, the second pump regulates more precisely the gas intake into the product. Therefore, control of the gas intake into the pumpable product can be made by controlling the speed of the second pump relative to the speed of the first pump, in particular, to set the desired quantity of the product coming out of the depositing device. For instance, the ratio of speed of the first pump to the speed of the second pump may be controlled within a range of from 1:1 to 1:5.
The pumps may be of very different types as typically used for transporting flowable liquid and viscous food. Preferably, the pumps are gear pumps, vane pumps, pawl pumps, centrifugal pumps or screw pumps.
The invention also relates to a method for aerating and depositing an aerated food comprising
pumping the food from a source of liquefied food,
adding gas from a source of gas in controlled amounts in the liquefied food to produce a gasified food;
maintaining a constant pressure of the gasified food up to depositing means including retaining means which retain the product at said pressure before the depositing point to prevent the product from expanding;
depositing amounts of the gasified food by forcing the product through the depositing point.